This invention concerns a tension screen with a screen area consisting of screen linings stretched over machine-mounted crossbars with a camber, where the screen linings have a plastic wear layer with screen passages and wire tension cables that run across the crossbars and are braced on the machine by means of connecting elements at the ends.
Tension screens of the aforementioned type are used especially for classifying course granular bulk materials such as mineral building materials, ores, etc. They are used in oscillating screen machines and consequently are exposed not only to rough operation but also to high dynamic stresses. In order to prevent wobbling of the screen linings, they are braced to the tension cables in the machine by means of connecting elements at the ends, in which case they rest on the crossbars running in the direction of the screen and have a camber in the middle.
These screen linings consist either of a wire cloth or more recently they are designed as plastic screens in which the tension cables are embedded in a castable plastic such as polyurethane. The tension cables project over the plastic wear layer at the sides and are secured to tension bars, etc., to which the tension forces acting on the machine are applied, by means of connecting elements.
Although plastic tension screens have better wear resistance and generate less noise in comparison with wire screens in many practical applications, they also have certain disadvantages. Since the entire screen surface is formed by a single screen lining, the entire screen must be replaced in the event of local wear or damage, so the lifetime is reduced and the investment cost is high accordingly. For the same reason, the screen lining must be manufactured in accordance with the given dimensions of the screen machine in the manufacturing operation and must be kept on stock there or by the operator of the screening machine. Furthermore, more rapid wear of the crossbars occurs at the contact points between the screen lining and the supporting crossbars where plastic is in contact with metal, while the plastic of the screen lining is relatively resistant. Consequently the crossbars must occasionally be serviced or even replaced and this is associated with a corresponding assembly expense.